1. Field of the Invention
The present invention relates to the field of networked access control devices.
2. The Background Art
Access control devices are known in the art. At their simplest level they consist of locks and keys used to control access to doors and the like. More recently networked access control devices have been developed which permit an entire system of access control to be controlled and maintained from a single point, such as a personal computer controller. Using such a networked access controller is a distinct improvement over prior technologies because of the ability to create a permanent record of access and egress including the identity of the person accessing and egressing as well as the time, the exact door or function accessed, and the like. Having a central control point allows easy re-keying of the system to add or delete authorized access.
In a typical access control situation, a door 10 as shown in FIG. 1 is equipped with a switch 12, typically a magnetically operated switch, which indicates if door 10 is open or closed. An electrically operated lock 14 controls access through the door. A magnetically coded card key 16 may be swept through a card key reader 18. If the card key 16 is valid, lock 14 will open permitting access through door 10. Alternatively, an RF proximity card reader or other type of access verification device may be used eliminating the need to sweep the card through the reader.
A typical network of access controllers is shown in FIG. 2. Master controller 20 is connected to slave controllers 22, 24 and 26 using a standard RS-485 network 28. The RS-485 network uses a shielded twisted pair (STP) medium such as Belden 9501 or equivalent. The RS-485 network 28 is a multipoint half-duplex differential data transmission network providing a capability of up to about 4000' or more of communication distance. It allows multiple nodes to communicate bidirectionally over a single twisted pair. In order to operate properly, each node on the network must have a unique address so that it will recognize messages sent to it.
Networked access systems as shown in FIG. 2 typically have one controller 20 designated as the master. This controller is located at one end of the RS-485 medium and is also connected to a host computer 30, either directly or through a modem 32. The host computer 30 runs software which allows an operator to configure and modify system parameters such as who is authorized to open which doors, hours of access, and the like. These parameters are then communicated over the RS-485 network to the various controllers 20, 22, 24, 26 which store the information on-board and operate relatively autonomously. The various controllers can transmit access event information back to the master 20 and then on to the host computer 30 which can display the information for use by an operator or record it for future use.
Turning to FIG. 3, a typical access controller 32 will have a connection 34 to the RS-485 network 36, a connection 38 to an access card key reader 40, proximity card key reader, or other access control device such as a keypad, or the like, a connection 42 to a door switch 44 indicating the status of the door, i.e., open or closed, a connection 46 to the door lock 48 or other device to be controlled, such as a parking lot gate arm, garage door, or the like, a connection 50 to a request to exit function 52 such as a button or proximity device used to permit egress when egress control is not required, a connection 54 to an alarm 56, if desired, to indicate an alarm condition such as attempted access or repeated attempted access with an invalid key, and optional connections 58 to optional devices 60 such as tamper detectors, additional access control devices, video surveillance devices and the like, as desired. Some controllers allow more than one door to be controlled from a single controller.
While present access control device controllers provide a good deal of functionality, they are very difficult to configure properly for installers in the field and a number of problems have been encountered in the field which have, in the past, caused difficulty in the installation process. In order to set the network address for known controllers, the field installer has to set a row of dip switches to the correct address desired for the controller. There is no indication of the address other than the state of the switches. If the switches are misconfigured, the installer has to go back to the controllers and check the dip switch configurations.
Similarly, the RS-485 network standard requires an end-of-line termination resistor across the differential conductor pair at the near and far end of the network medium. Typically each controller comes with the termination resistors on board to do this and they are placed in the circuit by the use of jumpers. Great difficulty has been experienced in the field in setting these jumpers to the correct position. If too many of the jumpers are left engaged, so that many controllers (more than one at each end of the network) are configured to apply their termination resistors across the conductors of the RS-485 medium, the network will become excessively loaded and will not operate reliably.
In order to insure proper operation of the network, it is desirable to bias the "+" and "-" conductors of the network medium through biasing resistors, the "+" side to Vcc (about +5 VDC) and the "-" side to ground. It is best to do this in a single place on the network. Using the jumper technology, frequently the network is loaded excessively with too many biasing resistors being active, or it is left biased in one direction only.
The shield of the network medium should be connected to earth ground at a single point . This provides the greatest immunity to noise. Since the prior art controllers provide a connection to earth ground via a jumper, it has been found that many installations have two or more connections of the shield to earth ground resulting in ground loops, noisy network connections and less than desirable system reliability.
Connecting the master controller to a computer has proved difficult in the past. Configuring switches and the like to tell the controller how it is to communicate with the computer has proved difficult in the field.
When using RF-type proximity card readers, ambient RF noise in the environment can disrupt the operation of the RF card reader. Without some way of detecting the presence of the noise, installers are frequently at a loss to explain why the entire system appears to be malfunctioning.
When installing controllers in locations subject to RF or induced currents, it is frequently difficult to diagnose problems caused by these environmental problems.